Etching procedures are widely used in the manufacturing of microelectronic and micromechanical devices to form features on a workpiece. The size of the individual components in the devices is decreasing and the number of layers in the devices is increasing. As a result, the density of the components and the aspect ratios of features are increasing to reduce the size of the individual dies and increase the performance. Moreover, the size of the workpieces is also increasing to provide more surface area for forming more dies on a single workpiece. Many fabricators, for example, are now using 300 mm workpieces, and even larger workpieces will likely be used in the future. As a result, etching techniques should produce highly uniform trenches, holes, and other features across the workpieces.
One challenge of plasma etching processes is to provide a uniform etch profile across the surface of a workpiece. Plasma etching systems typically include a reaction chamber, a gas distributor, and a chuck. In one type of plasma etching system, the gas distributor typically is electrically conductive and defines one electrode and the chuck is often another electrode for forming a plasma. The plasma includes a variety of reactive species (e.g., ionized and/or dissociated species) corresponding to a specific process gas provided by the gas distributor. These reactive species physically and/or chemically etch the surface of the workpiece. In general, the chamber, the chuck, and the plasma can have a variety of thermal, electrical, and/or chemical properties that affect the rate at which the reactive species remove material from the workpiece. If the properties of the plasma vary relative to the workpiece surface, this can in turn create non-uniform etch rates across the workpiece surface and other variations in etching parameters.